Gas turbines and their associated compressors are operated at high temperatures and pressures and it is necessary for reasons of safety and efficiency that their housings or casings should securely contain the pressurized gases within. The housings are manufactured in several parts so an effective seal is required at the joints or junctions between those parts. Such seals must function under extreme conditions, particularly in the case of turbine housings, and must be able to accommodate relative movement between the housing parts caused by vibration and by differential thermal expansion during operation of the turbomachine.
In an existing sealing arrangement between two adjacent parts of a generally cylindrical turbine housing, one part of the housing is formed to have an annular recess facing radially inwards; and the other part of the housing is formed to have an annular recess facing radially outwards opposite the first annular recess. An annular seal plate lying in a diametric plane centered on the turbine axis has its outer edge tightly fitted into the first recess and its inner edge tightly fitted into in the second recess to form a seal between the two housing parts. This arrangement can accommodate some circumferential movement of the seal plate. To accommodate relative axial movement between the two housing parts, the recesses can be given a bird-mouth cross section or the seal plate can be given a dog-bone cross section, either of which arrangements allows the seal plate to deform from the radial plane without breaking the seal.
A problem with this known sealing arrangement is that the relative movement between the seal plate and the housings causes wear on the seal plate and in the recesses, which leads to a degraded sealing function. The seal plate can be replaced relatively easily and cheaply during regular maintenance of the gas turbine, but wear to the housing is more serious because that housing parts are large, complex and expensive components and it is desirable to replace them as infrequently as possible.
For ease of explanation, the housing was described above as “cylindrical” and the seal plate between the housing parts as “annular”. Note that in the present specification, terms such as “cylindrical”, “annular” and “ring” should not be limited to perfectly circular components but should be interpreted to include other closed curves where good engineering practice so permits.